That tool is designed for long, consistent bends. I used it for making a covered parking spot for my car with 1/2" sqaure tubing:
I also used it for the curved piece on this workbench:
You can see I had to do some helper cuts with the heavier stock (and the wrong dies).
Still, it came out looking cool:
But a roll bender is definitely not something you'd want to use for 90° bends like you'd see in a roll cage. For that, you use one of HF's benchtop or freestanding benders, like this:
HF also makes one that attaches to a benchtop. In either case, you're going to have to find some dies that will work with it (since HF only has pieces for solid stock, I think).
Or watch for a used Hossfeld or a JD2 (probably the best bang for the buck) -- or make your own from plans (for even more bang). Lots of threads on this.